The Working Group for Civilian Biodefense reviewed potential biological threat agents and listed those considered to pose the greatest threat to the civilian population. Variola and other orthopox DNA viruses were identified as a potential bioterrorism threat. Additionally, other DNA viruses are of increasing concern in a public health context due to the emergence of new pathogens and the potential for development of drug resistance among currently recognized viruses. Thus, the development of new, more effective broad-spectrum antiviral compounds against category A-C and emerging pathogens is a high priority for NIAID. The DNA viruses, which include herpes-, adeno-, pox-, polyoma- and papillomaviruses, have a requirement for DNA synthesis during their life cycle. This common element therefore becomes a common target for broad-spectrum antiviral compounds. The nucleoside phosphonates (NP), exemplified by HPMPA and cidofovir, have shown strong activity across a wide spectrum of DNA viruses. However, their development as antiviral drugs has been hampered by their inherent lack of bioavailability due to their highly polar nature. Our research efforts have centered on overcoming the lack of oral bioavailability and low cellular permeability of available broad-spectrum antiviral cyclic and acyclic nucleoside phosphonate (CNP and ANP) drugs by means of a novel prodrug strategy. In the Phase I portion of the project, these efforts have yielded a lead series of prodrugs of HPMPC (cidofovir) and HPMPA with greatly enhanced in vitro antiviral potency against several DNA viruses, good oral absorption and significantly reduced risk of toxicity. In this Phase II SBIR project, we propose to screen the lead compounds by fully characterizing their PK properties, testing their in vivo efficacy in a number of acceptable animal models and measuring their toxicity in order to select a lead compound to take forward into the clinic. The proposed program is based upon an established drug research partnership between Dr. John Hilfinger at TSRL, Inc. and Professor Charles McKenna at the University of Southern California and will draw upon essential and unique virological expertise from collaborators located at the University of Alabama Birmingham, Cincinnati Children's Hospital, St. Louis University, Utah State University, and SUNY Medical Center.